The price of ammo is a big factor. In the last year or so a good many people who were shooting the .357 Sig (experimenting with it mainly) and the 40 have dropped off shooting those and gone to the 9mm. Often that's justified by saying the 9mm is "just as good", etc. But price has been a big consideration. Sometimes it's the perception of price. Plinking/practice ammo for the 9mm is less expensive